Typically, in the radio communication system, a space diversity can be acquired through multiple independent paths between transmitters (source nodes) and receivers (destination nodes) that are relative to space-time codes (STC). Further, if a relay node is used, there are additional independent paths between the transmitters and the receivers, penetrating the relay node. Such a system is called a cooperative network. In this case, a cooperative diversity is acquired. In a two-phase cooperative protocol of the cooperative network, the source node transmits signals to the relay node or the destination node at a first phase (or timeslot) and the relay node transmits signals to the destination node at a second phase. The protocol is called a non-orthogonal protocol or an orthogonal protocol according to whether the source node continually performs the transmission at the second phase.
Recently, studies on the cooperative network have been widely conducted. In a paper, J. N. Laneman and G. W. Wornell, “Distributed space-time-coded protocols for exploiting cooperative diversity in wireless networks,” IEEE Trans. Inform. Theory, vol. 49, pp. 2415˜2425, October 2003, repetition and space-time algorithms has been suggested to acquire the cooperative diversity. Moreover, in a document, Y. Jing and B. Hassibi, “Distributed space-time coding in wireless relay networks,” IEEE Trans. Wireless Commun., vol. 5, no. 12, pp. 3524˜3536, December 2006, a distributed STC (DSTC) for an amplify-and-forward (AF) protocol by using a two-hop system has been suggested. If transmission power is infinitely great, in the scheme, when R relay nodes are used, the diversity order R is acquired. In a paper, Y. Jing and H. Jafarkhani, “Using orthogonal and quasi-orthogonal design in wireless relay networks,” IEEE Trans. Inform. Theory, vol. 53, no. 11, pp. 4106˜4118, November 2007, practical DSTCs has been designed by using orthogonal space-time block codes (OSTBCs) and quasi-orthogonal space-time block codes (QOSTBCs) for the AF protocol. In a paper, B. Maham and A. HjÁungnes, “Distributed GABBA space-time codes in amplify-and-forward cooperation,” in Proc. ITW 2007, July 2007, there has been suggested the design of the DSTCs performed by using generalized QOSTBCs. Here, any relay nodes can be used to increase the diversity order. Moreover, a suboptimal linear decoder can be used to acquire a maximum diversity order and reduce the complexity. In a paper, Y. Jing and B. Hassibi, “Cooperative diversity in wireless relay networks with multiple antenna nodes,” in Proc. ISIT'05, pp. 815˜819, September 2005, the DSTCs for the AF protocol have expanded to the cooperative network by a multiple antenna. In a paper, G. S. Rajan and B. S. Rajan, “A non-orthogonal distributed space-time coded protocol—Part 1: Signal model and design criteria,” in Proc. ITW'06, pp. 385˜389, March 2006, there has been suggested a non-orthogonal AF (NAF) protocol generalized by using a single antenna in the source node, the relay node, and object node, respectively. They prove that 3 other protocols have the same diversity order R+1. Here, a first protocol and a second protocol are identical to the NAF protocol and the orthogonal AF (OAF) protocol, respectively. The reason that they have the same diversity order is that signals including same information transmitted from the source node undergo same fading at the first and second phases.
In such aforementioned protocols, the source node signals to the relay nodes and the destination node at the phases. At the first phase, the source node transmits a STC and the relay node transmits a re-encoded STC by using a signal decoded from the received signal. However, even through the source node transmits the signal two times at the first and second phases. Since a source-destination (SD) channel is the same at the first and second phases, the DSTCs may not increase the diversity order.